NomenclatureThe symbol 'Ku' refers to Kurz-unter (German) which mean below the K-band. Likewise the symbol 'Ka' refers to K-above meaning above the K-band.
As more of the world migrates towards using wireless technology each day, optimal, high-speed, and reliable wireless connectivity has become the need of the hour. The advanced High Throughput Satellites (HTS) have been designed to take care of these requirements.
HTS technology boasts an unprecedented bandwidth capability, and is widely viewed as the future of satellite communications. Typically for HTS systems, the Ku-band or the Ka-band of the electromagnetic spectrum are used.
In recent years owing to the explosion in Internet based applications, the demands for higher satellite capacity has skyrocketed. The capacity of the lower Ku-band of the spectrum is falling short, and investments are now being made in the use of the Ka-band. These bands are not interchangeable, and each has its own advantages and disadvantages, which makes it suitable for one set of applications and unsuitable for another.
In the following sections, we shall examine the differences between Ka-band and Ku-band. But, before that, we shall learn more about the HTS systems.
High Throughput Satellites (HTS)
In the High Throughput Satellites system, the coverage area is divided into small regions known as spots. Each spot is then served by a spot beam. This is unlike the conventional system where one large beam is used to serve the entire area of coverage.
Each spot beam covers an area that is only about 1% to 2 % the size of the conventional beam. This allows these beams to provide high signal strength as well as gain. Thus overall performance is better than that of the conventional system.
Newer advanced technology also allows more accurate antennas to be built and thus the spots can be made smaller. This makes it possible to reuse frequencies multiple times, making HTS satellites more efficient.
The Ku band refers to the band of electromagnetic frequencies in the range of 12-18 GHz. It is located directly below the K-band.
This band is mainly used for fixed as well as broadcast satellite communication services. It is also used in specific applications such as in communications between space shuttle and the International Space Station (ISS), as well as radar applications.
The Ka-band of the electromagnetic spectrum comprises frequencies in the range of 26.5-40 GHz. This band is located directly above the K-band.
The frequencies in this band are used for close-range military radars, vehicle speed detection, and few other specific applications. NASA's Kepler mission utilizes frequencies in this band to down-link scientific data collected by the space telescope.
Ka-band Vs. Ku-band
Availability of Spectrum
The C-band and Ku band of the electromagnetic spectrum have been around for a long time. As such, there are an extensive number of satellites and services which use frequencies in these bands.
Compared to this, the use of frequencies in the Ka-band has only recently started gathering steam. This fact, coupled with the frequency-reuse capability of the multiple spot beam technology of the HTS, increases the usable spectrum that is available.
The Ka-band satellites which are currently in orbit serve only specific and limited geographical regions. For example, the ViaSat-1 launched in 2011, only provides coverage to North America. Similarly, the KA-Sat launched in 2010 serves only Europe, the Mediterranean basin, and small regions in the Middle East.
Obviously, none of these are a viable option for ships or intercontinental airplanes, which need to traverse the non-covered oceanic zone. Also, due to the receding polar ice caps, in recent years, vessels have begun traversing the now navigable Northeast and Northwest passages. The current Ka-band satellites are incapable of providing coverage to them.
Ku-band satellites, on the other hand, are more in number and have a much wider coverage area in comparison to Ka-band satellites. Further, satellites communicating over the lower L-band, presently are a more viable option for most ocean-going vessels.
The Ku-band satellites are often placed as little as two degrees apart from each other in the Earth's orbit. This increases the chances of adjacent satellite interference.
The Ka-band satellites are placed further apart from each other, and therefore, the chances of antennas transmitting to non-targeted satellites and interference between signals is much less.
The size of antenna is inversely proportional to the frequency band of the signal it transmits or receives. Hence, smaller-sized antennas can be used for the systems that operate on the Ka-band as compared to the ones used for the Ku-band. Since the antenna sizes are smaller, their cost too would be lower. They should also be easier to install.
The frequencies in the Ka-band are nearly double that of the frequencies in the Ku-band. Since wavelength is inversely proportional to frequency, the wavelengths of signals in the Ka-band are much smaller than those of the Ku-band. This makes them more susceptible to bad weather and other atmospheric disruptions.
Rains drops are known to absorb signals having frequency above 11 GHz. This effect is known as rain-fade. Snow and ice too absorb these high frequency signals. Both Ku-band and Ka-band signals suffer from rain fade; however, the fading is larger for Ka-band signals owing to their higher frequencies.
Since there are a number of satellites currently in orbit which function on the Ku-band, there won't be a problem finding a backup satellite to maintain a continuous link in case the main satellite develops a fault.
However, in comparison, there are far fewer satellites that function in the Ka-band of the spectrum, and the ones that do, are often part of a closed network. So, in the event of failure, it will be very difficult to find a backup satellite to maintain the communication link.
Due to lower demand, Ka-band-capable equipment are less common in the market as compared to Ku-band-capable equipment. Therefore, the cost of Ka-band equipment and systems typically is higher than the Ku-band ones.
It is true that, at present, systems designed specifically for direct-to-home users are becoming available to a wider market. This may decrease the equipment cost as sales volume increases. However, currently, the cost of equipment and components remain on the higher side.
The use of signals in the Ka-band is clearly the next step in the evolution of satellite communication. Considering the higher bandwidth requirements of today, one can even say that it is a necessity. However, that doesn't mean that it will abolish the Ku-band operations. Even though the technological shift towards higher frequency signals will continue to push many more applications to communicate in the Ka-band in the future, the Ku-band, like the C-band and the L-band before it, will continue to remain important and reliable options.